The invention pertains to flat-panel electronic displays and, more particularly, to large, flat-panel electronic displays that are composed of a plurality of joined, smaller building blocks (tiles) having seams therebetween. The tiles may be viewed as though they were a single, monolithic display (i.e., as a display having visually imperceptible seams).
Images on electronic displays are derived from an array of small picture elements known as pixels. In color displays, these pixels comprise three color elements that produce the primary colors: red, blue and green (R, B and G), for example. Usually arranged in rectangular arrays, these pixels can be characterized by a pixel pitch, P, a quantity that measures the spacing of pixels in one direction. A typical cathode-ray tube (CRT) display used for computer applications has a pixel pitch of 0.3 mm and a pixel array width:height ratio of 4:3. Typical standardized arrays in computer displays are comprised of 640xc3x97480 video graphics array (VGA) or 800xc3x97600 pixels super video graphics array (SVGA), 1024xc3x97768 extended graphics array (XGA) and new standards are being generated with 16/9 ratios, wide screen format, such as standard definition television (SDTV) 852xc3x97480 and high definition television (HDTV) 1280xc3x97720.
Large displays can be constructed of a plurality of adjacent tiles, with each having a single pixel or an array thereof. Such assembled tiled displays contain visually disturbing seams, resulting from the gaps between adjacent pixels on the same and/or adjacent tiles. Such seams may incorporate interconnect, adhesives seals, mechanical alignment means and other components resulting in visible optical discontinuities in displayed images. Some of these structures are described in the aforementioned U.S. Pat. No. 5,661,531. As a consequence, the image portrayed on seamed displays appears segmented and disjointed. Therefore, it is desirable to fabricate tiled, flat-panel displays which do not have noticeable or perceptible seams under the intended viewing conditions.
The pixel pitch in electronic displays must be set so that a continuous image is produced when the display is viewed at distances greater than the minimum viewing distance. For example, with a pixel pitch of P=0.3 mm, the minimum viewing distance is on the order of 1 m. Even though the minimum viewing distance increases in proportion to the pixel pitch, it still limits the pixel pitch for most computer and consumer displays. Since space for the tiling functions must be provided in areas within the pixel pitch but smaller in size than the pixel pitch, it is difficult to develop structures and methods for constructing tiled visually seamless displays.
Flat-panel displays (FPD) provide the best choice for constructing xe2x80x9cseamlessxe2x80x9d, tiled screens. Flat-panel displays include backlighted and self-lighted displays. Liquid crystal displays (LCDs) are the most common backlighted displays.
Flat-panel displays depend on the microfabrication of key components that carry the pixel patterns. Unfortunately, microfabrication techniques are not viable for very large displays currently greater than 20 inches diagonal, due to the fact that manufacturing yield declines rapidly with increasing area of the display. Furthermore handling and filling the largest Active Matrix Liquid Crystal Display (AMLCD) displays with liquid crystal increases yield losses. Therefore, the inventors have determined that tiles with arrays of pixels can be microfabricated and then assembled together to form a larger electronic display.
The present invention provides unique designs and methods for achieving such large, seamless, tiled panels for color or gray-scale displays. This invention particularly focuses on displays of the transparent, lightvalve type. In such displays, light from a uniform, backlight source is transmitted through the display assembly and directly viewed from the front side of the display. The lightvalves control the amount of primary light rays transmitted through each of the color elements in the pixels. At a sufficient viewing distance, the viewer""s eyes merge the primary light from the pixels to form a continuous image. Because of a number of secondary processes, low-level light emanates from the spaces between the pixels. These phenomena include reflection and light guiding, all of which must be kept to a minimum in order to achieve sufficient brightness and contrast. The spaces between pixels on the same tile, and the spaces between pixels on adjacent tiles have different structures. Consequently, the presence of seams between the pixels at the edge of the tiles affects both primary and secondary light rays, thus increasing the difficulties for constructing seamless, tiled displays.
The inventors have identified three design principles in making large-scale, seamless, flat panels that may be viewed as though they were single monolithic displays: (a) the intra-tile pixel pitch on the view plane for the tiles must be substantially matched to the inter-tile pixel pitch; (b) the primary light paths through the lightvalves must not be affected by the presence of the seam or any other structures or components used in the tile assembly; (c) the inter-pixel regions must be designed so that intra-tile and inter-tile pixel regions, which have different physical structures, present approximately the same visual appearance to the viewer under transmitted and reflected light. This has largely been accomplished by applying the technology described in U.S. Pat. No. 5,661,531 to fabricated tiled AMLCD functional models. These functional prototype models of a 2xc3x972 array of AMLCD tiles are SVGA FPDs with 38.6 diagonal view areas that have monolithic seamless appearance in static and video modes. However, design improvements in this patent disclosure will increase manufacturing yields and maximize optical performance for SDTV and HDTV application of the tiled displays and their component parts, particularly the tiles. It is also possible with this invention to build dual usage displays such as a display that can provide either HDTV or XGA formats.
The present invention describes a tiled, flat-panel display having visually imperceptible seams between tiles disposed in an interior portion thereof, so that the display is perceived by a human observer as a single, monolithic display, when viewed at a distance equal or greater than the intended minimum viewing distance. This invention applies primarily to lightvalve-type, flat-panel displays with a backlight.
The panel comprises an image source plane having spaced-apart pixels with active areas which control the primary-color, light-transmitting elements (e.g., red, blue and green). It should be understood that the primary colors need not be red, blue and green but may be other colors, and not necessarily limited to three. Included in the image source plane may be a color filter (CF) layer. Alternatively, the CF may be included with screen and polarizer outside of the tiles continuous across the mosaic. Surrounding the active area of each pixel is an inactive (dark) area. This dark area can be used for a variety of purposes without affecting the light output and/or visual appearance of the display. For example, electrical circuitry, such as transistors, are situated in the dark spaces. Most importantly, thin, perimeter seals at the edges of the AMLCD tiles may utilize that portion on the dark areas of the pixels adjacent to the edge. Wiring may also be placed in the pixel dark areas, as required.
Each of the pixels is disposed along the image source plane at a given pitch greater than approximately 0.2 mm and preferably in a range of 0.7 to 1.0 mm, depending upon the size of the display and the pixel density desired. An image source plane is defined by the plurality of adjacently-disposed tiles. The invention includes a number of methods for the design, construction and assembly of tiled displays with invisible seams which are significant compliments to the technique disclosed in U.S. Pat. No. 5,661,531 etc. These can be grouped into the following distinct categories: (1) alteration of the characteristics of the image source plane, (2) preferred positioning and design of the masks, polarizer and image view plane (screen) to enhance hiding of the seams between tiles, (3) optimizing the pixel design, the seal control factors, the row and column wiring, (4) enhancement of the brightness of the display assembly by optimizing the backlight collimation angles, (5) enhancement of the brightness and contrast of the display assembly by optimizing the design of the collimation angles and (6) improvement in positioning of the subpixels to improve directional color matching between tiles. This patent will be focused on optimization of these factors for large flat panel displays assembled from a 1xc3x97N array of AMLCD tiles.